1. Field of the Invention
The present invention generally relates to a disk drive, and more particularly to a technique which determines a track pitch for writing servo information on a disk medium.
2. Description of the Related Art
Generally, a disk medium on which servo information for head positioning is recorded in advance is incorporated in a disk drive as typified by a hard disk drive. The servo information is recorded by a servo track writer (STW) in a disk drive manufacturing step.
In a servo write step, there is a self-servo write mode by which servo information is recorded on a disk medium in a disk drive itself (e.g., see U.S. Pat. No. 5,581,420).
In the self-servo write mode, in order to determine a head feed pitch quantity when recording a servo pattern, processing for determining a servo track pitch is required. A method of determining a track pitch disclosed in a prior art reference determines a next track pitch by comparing intensities of reproduction amplitudes of servo burst patterns at the time of a write operation in a write-once-read-multiple mode.
However, a reproduction amplitude which is output from a head varies depending on a position of a head in a radial direction (radial position) which falls in an inner/outer peripheral range on a disk medium. As its factors, there can be considered a flying height of a head, a recording resolution of a disk medium, settings of a band filter of a servo decoder, an influence of an amplitude equalization filter and others. Therefore, the method of determining a servo track pitch by comparing reproduction amplitudes of servo burst patterns has a possibility that this track pitch varies depending on a radial position of a head.
In order to solve such a problem, there has been proposed a method which takes a fact that a servo signal reproduction output varies depending on a flying height or a radial position of a head into consideration and changes a reference value of a track pitch in accordance with each head or a zone (e.g., see U.S. Pat. No. 6,181,504).
However, this method disclosed in the reference presupposes that servo information is written on an entire surface of a disk medium, and it is not suitable for the self-servo write mode which determines a track pitch while writing servo information.
In the method disclosed in each prior art reference mentioned above, a measurement position which is required to determine a track pitch is defined as an intermediate point between a center of a servo burst pattern and a center of a servo burst pattern adjacent to the former pattern. Therefore, processing for moving a head to a specified position is required for the purpose of track pitch determination processing, and the servo writing processing efficiency is lowered in the self-servo write mode.